[PATCH] f2fs: avoid migratepage for atomic written page

[Jaegeuk Kim]

In order to avoid lock contention for atomic written pages, we'd better give
EAGAIN in f2fs_migrate_page. We expect it will be released soon as transaction
commits.

Signed-off-by: Jaegeuk Kim <jaeg...@kernel.org>
---
 fs/f2fs/data.c | 35 ++++++++++-------------------------
 1 file changed, 10 insertions(+), 25 deletions(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index d58b81213a86..1458e3a6d630 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -2197,41 +2197,26 @@ static sector_t f2fs_bmap(struct address_space 
*mapping, sector_t block)
 int f2fs_migrate_page(struct address_space *mapping,
                struct page *newpage, struct page *page, enum migrate_mode mode)
 {
-       int rc, extra_count;
-       struct f2fs_inode_info *fi = F2FS_I(mapping->host);
-       bool atomic_written = IS_ATOMIC_WRITTEN_PAGE(page);
+       int rc;
 
-       BUG_ON(PageWriteback(page));
-
-       /* migrating an atomic written page is safe with the inmem_lock hold */
-       if (atomic_written && !mutex_trylock(&fi->inmem_lock))
+       /*
+        * We'd better return EAGAIN for atomic pages, which will be committed
+        * sooner or later. Don't botter transactions with inmem_lock.
+        */
+       if (IS_ATOMIC_WRITTEN_PAGE(page))
                return -EAGAIN;
 
+       BUG_ON(PageWriteback(page));    /* Writeback must be complete */
+
        /*
         * A reference is expected if PagePrivate set when move mapping,
         * however F2FS breaks this for maintaining dirty page counts when
         * truncating pages. So here adjusting the 'extra_count' make it work.
         */
-       extra_count = (atomic_written ? 1 : 0) - page_has_private(page);
        rc = migrate_page_move_mapping(mapping, newpage,
-                               page, NULL, mode, extra_count);
-       if (rc != MIGRATEPAGE_SUCCESS) {
-               if (atomic_written)
-                       mutex_unlock(&fi->inmem_lock);
+                       page, NULL, mode, (page_has_private(page) ? -1 : 0));
+       if (rc != MIGRATEPAGE_SUCCESS)
                return rc;
-       }
-
-       if (atomic_written) {
-               struct inmem_pages *cur;
-               list_for_each_entry(cur, &fi->inmem_pages, list)
-                       if (cur->page == page) {
-                               cur->page = newpage;
-                               break;
-                       }
-               mutex_unlock(&fi->inmem_lock);
-               put_page(page);
-               get_page(newpage);
-       }
 
        if (PagePrivate(page))
                SetPagePrivate(newpage);
-- 
2.13.0.rc1.294.g07d810a77f-goog